Xiangyuan Zeng

Solar Sail Body-Fixed Hovering over Elongated Asteroids

Solar sail spacecraft are proposed to accomplish body-fixed hovering missions over elongated asteroids. The body-fixed hovering flight is to maintain a fixed position relative to the surface of the spinning asteroid. A solar sail without fuel consumption can greatly expand the range of hovering locations in a variable lightness number for an extended period. A rotating mass dipole is used to produce the gravitational field created by an elongated asteroid. Dynamic equations are obtained for the approximate model in terms of the specified hovering conditions. Feasible hovering regions over elongated asteroids are presented and analyzed via numerical simulations. A parametric study is made to investigate the influence of solar latitude angles and the lightness number on the feasible hovering region. The hovering orbits around the realistic asteroid 951 Gaspra are performed to evaluate the effectiveness of the method in this paper.

Feasible region and stability analysis for hovering around elongated asteroids with low thrust

This paper investigates properties of low-thrust hovering, including the feasible region and stability, in terms of the dynamical parameters for elongated asteroids. An approximate rotating mass dipole model, by which the description of the rotational gravitational field is reduced to two independent parameters, is employed to construct normalized dynamical equations. The boundaries of the feasible region are determined by contours representing the magnitude of the active control. The effects of a rotating gravitational field and maximal magnitude of the low thrust on the feasible hovering regions are analyzed with numerical results. The stability conditions are derived according to the forms of the eigenvalues of the linearized equation near the hovering position. The stable regions are then determined by a grid search and the effects of the relevant parameters are analyzed in a parametric way. The results show that a close hovering can be easier to realize near the middle of the asteroid than near the two ends in the sense of both required control magnitude and stability.

Asteroid body-fixed hovering using nonideal solar sails

Asteroid body-fixed hovering problem using nonideal solar sail models in a compact form with controllable sail area is investigated in this paper. The nonlinear dynamic equations for the hovering problem are constructed for a spherically symmetric asteroid. The feasible region for the body-fixed hovering is solved from the above equations by using a shooting method. The effect of the sail models, including the ideal, optical, parametric and solar photon thrust, on the feasible region is studied through numerical simulations. The influence of the asteroid spinning rate and the sail area-to-mass ratio on the feasible region is discussed in a parametric way. The required sail orientations and their corresponding variable lightness numbers are given for different hovering radii to identify the feasibility of the body-fixed hovering. An attractive mission scenario is introduced to enhance the advantage of the solar sail hovering mission.

New applications of the H-reversal trajectory using solar sails

Advanced solar sailing has been an increasingly attractive propulsion system for highly non-Keplerian orbits. Three new applications of the orbital angular momentum reversal (H-reversal) trajectories using solar sails are presented: space observation, heliocentric orbit transfer and collision orbits with asteroids. A theoretical proof for the existence of double H-reversal trajectories (referred to as ‘H2RTs’) is given, and the characteristics of the H2RTs are introduced before a discussion of the mission applications. A new family of H2RTs was obtained using a 3D dynamic model of the two-body frame. In a time-optimal control model, the minimum period H2RTs both inside and outside the ecliptic plane were examined using an ideal solar sail. Due to the quasi-heliostationary property at its two symmetrical aphelia, the H2RTs were deemed suitable for space observation. For the second application, the heliocentric transfer orbit was able to function as the time-optimal H-reversal trajectory, since its perihelion velocity is a circular or elliptic velocity. Such a transfer orbit can place the sailcraft into a clockwise orbit in the ecliptic plane, with a high inclination or displacement above or below the Sun. The third application of the H-reversal trajectory was simulated impacting an asteroid passing near Earth in a head-on collision. The collision point can be designed through selecting different perihelia or different launch windows. Sample orbits of each application were presented through numerical simulation. The results can serve as a reference for theoretical research and engineering design.

Trajectory optimization and applications using high performance solar sails

The high performance solar sail can enable fast missions to the outer solar system and produce exotic non-Keplerian orbits. As there is no fuel consumption, mission trajectories for solar sail spacecraft are typically optimized with respect to flight time. Several investigations focused on interstellar probe missions have been made, including optimal methods and new objective functions. Two modes of interstellar mission trajectories, namely “direct flyby” and “angular momentum reversal trajectory”, are compared and discussed. As a foundation, a 3D non-dimensional dynamic model for an ideal plane solar sail is introduced as well as an optimal control framework. A newly found periodic double angular momentum reversal trajectory is presented, and some properties and potential applications of this kind of inverse orbits are illustrated. The method how to achieve the minimum periodic inverse orbit is also briefly elucidated.

Utilization of an H-reversal trajectory of a solar sail for asteroid deflection

Near Earth Asteroids have a possibility of impacting the Earth and always represent a threat. This paper proposes a way of changing the orbit of the asteroid to avoid an impact. A solar sail evolving in an H-reversal trajectory is utilized for asteroid deflection. Firstly, the dynamics of the solar sail and the characteristics of the H-reversal trajectory are analyzed. Then, the attitude of the solar sail is optimized to guide the sail to impact the target asteroid along an H-reversal trajectory. The impact velocity depends on two important parameters: the minimum solar distance along the trajectory and lightness number of the solar sail. A larger lightness number and a smaller solar distance lead to a higher impact velocity. Finally, the deflection capability of a solar sail impacting the asteroid along the H-reversal trajectory is discussed. The results show that a 10 kg solar sail with a lead-time of one year can move Apophis out of a 600-m keyhole area in 2029 to eliminate the possibility of its resonant return in 2036.

Earth-Crossing Asteroid Intercept Mission with a Solar Sail Spacecraft

A falling meteor that blazed and exploded over the Russian Ural Mountains on February 15, 2013, has been attracting attention from all over the world. It was estimated by the Russian Academy of Science and the U.S. National Aeronautics and Space Administration (NASA) that the meteor entered Earths atmosphere at a speed of approximately 33-40 km/s. The energy released by the meteor is on the level of hundreds of kilotons of TNT. The threat posed by such falling meteors and Earth-crossing asteroids (ECAs) cannot be excluded as one of the most unpredictable risks to Earth and humans.

Earth-Crossing Asteroids Deflection with a Sailcraft

Fast intercept trajectories are discussed to impact the dangerous Earth-crossing asteroids by using a solar sail spacecraft for the near to far-term missions. The heliocentric trajectory with a single solar photonic assist is considered to transfer the sail kinetic impactor from the Earth orbit to the collision point with the asteroid. Two options of such trajectories, i.e., the direct flyby and the angular momentum reversal trajectory, are compared via numerical simulations with respect to the transfer time and the relative collision velocity to determine which one is more suitable. The variation trend of the relative collision velocities are presented for different mission scenarios as a function of the sail lightness number. For a square flat ideally reflective sail with a given assembly loading, the determination of the impactor mass is studied to obtain the highest value of the net increment velocity of the asteroid.